Method and apparatus for preventing coke obstructions in pyrolysis plants

ABSTRACT

An apparatus for the prevention of coke obstruction in a pyrolysis plant, for example in the cracking of ethane in the manufacture of ethylene, wherein cracked gases from a pyrolysis furnace at a temperature of 750* to 850* C. are passed to a cooler and a screen is disposed in the inlet portion of the cooler at an easily accessible portion whereby the on stream line of the pyrolysis stream is extended.

United States Patent [1 Schneider et al.

[ Nov. 13, 1973 METHOD AND APPARATUS FOR PREVENTING COKE OBSTRUCTIONS IN PYROLYSIS PLANTS [75] Inventors: Hans Schneider; RichardGustav Hussner, both of Heide/Holst; Raimund Erhard Fischer, Hemmingste'dt, all of Germany [73] Assignee: Deutsche Texaco Aktiengesellschaft,

Hamburg, Mittelweg, Germany 22 Filed: Dec. 3, 1970 21 Appl. No.: 94,734

[52] US. Cl 196/98, 55/267, 55/307,

55/521, 55/529, 55/DIG. 2O [51] Int. Cl B01d 46/00 [58] Field of Search 55/1, 267, 268, 269,

55/307, 308, 385, 318, 320, 321, 323, 331, 332, 333, 334, 335, 336, 463, 368, DIG. 20; 202/96, 152, 163, 180, 182, 185, 197, 200; 196/98 [56] References Cited UNITED STATES PATENTS 36,619 10/1862 Marks et a1 55/335 127,966 6/1872 Radley 55/D1G. 20 132,179 10/1872 Radley 55/D1G. 20 367,413 8/1887 Koch 55/308 X 378,762 2/1888 Brown 55/D1G. 20 955,504 4/1910 Dunlap et al. 55/DIG. 20 1,126,692 2/1915 Blanchette 55/307 X 1,281,142 lO/l9l8 2,068,332 l/1937 Kneisley 55/368 X Primary Examiner-Dennis E. Talbert, Jr. AttorneyThomas H. Whaley, Carl G. Ries and H. L. Madinger [5 7 ABSTRACT An apparatus for the prevention of coke obstruction in a pyrolysis plant, for example in the cracking of ethane in the manufacture of ethylene, wherein cracked gases from a pyrolysis furnace at a temperature of 750 to 850 C. are passed to a cooler and a screen is disposed in the inlet portion of the cooler at an easily accessible portion whereby the on stream line of the pyrolysis stream is extended.

1 Claim, 1 Drawing Figure Illlll Ill IlIIlll ll I Illlll METHOD AND APPARATUS FOR PREVENTING COKE OBSTRUCTIONS IN PYROLYSIS PLANTS BACKGROUND OF THE INVENTION In the known processes the hot olefin-containing cracked gases leaving the pyrolysis furnace are passed through a cooler and/or a quenching zone. The pyrolysed gases form coke inside the cooler, which is then separated. At the inlet of the heat exchanger surfaces of the cooler and on said surfaces the coke deposits in a firm crustlike layer or coating continuously increasing in thickness, which results in an ever reduced heat exchange, eventual obstructions and close-down of the plant. It is difficult and costly to remove these coke crusts, as the customary coolers have large heat exchange surfaces arranged over a minimum space.

There are tests known by which to obviate coke crust formation by measures derived from flow technique. This involves cooler inlets being equipped with devices whereby the rate of flow of the cracked gases is kept constant across the section of the cooler. Without these devices the coke crust formation used to be irregular across the section of the cooler, i.e. certain areas in the cooler were covered much faster by coke crusts than were others. With these devices coke crust formation proceeded at an equal rate across the section of the cooler, however, the times needed for covering certain parts of the cooler were slightly prolonged. Thus the close-down of the cooler was, not prevented, but delayed.

SUMMARY OF THE INVENTION The present invention relates to an improvement of methods for the recovery of olefins from saturated hydrocarbons by means of pyrolysis. It further relates to any other method for pyrolysing organic compounds in the gaseous phase, in which separation of coke is to be expected.

It is an object of this invention to prevent or considerably delay coke obstruction of the cooler, in order to extend many times the running times of the furnaces. It is another object of this invention to prevent coke obstruction of other parts of pyrolysis plants.

The present invention has solved these problems by a device for preventing coke obstructions in pyrolysis plants, characterized by causing the coke to deposit at an easily accessible point in the cracked gas stream between the pyrolysis furnace and the cooler by arranging at said point a screen or sieve medium. Surprisingly, the formation of coke crusts now concentrates on this sieve medium and no longer occurs on the parts of the pyrolysis plant arranged behind the sieve medium, as seen in the direction of flow of the cracked gas stream.

The sieve medium of this invention may consist of a hollow structure of wire mesh or a structure consisting of several wire mesh disks. It is also possible to use irregularly joined filaments or even filament balls. Other materials may also be used in place of wire, e.g. ceramic bars or ceramic splinters as packing combined in a wide-meshed flat two-r three-dimensionally extended sieve medium. According to this invention anyone skilled in the art may manufacture a sieve medium such that it presents as large a surface as possible to the cracked gas stream and yet allows said gas stream to pass through.

wall being more or less fitted to the cooler inlet head.

Another embodiment of this invention consists of several wire mesh cages fitted into each other, with the cage meshes increasing in size from the outer to the inner cages. A double cage, wherein the inner cage has wider meshes than the outer cage, is of particular advantage.

According to this invention the sieve medium is removed from the plant as soon as coke crust formations noticeably impede the flow of the cracked gas stream, and is replaced by a new coke-free sieve medium. According to this invention means for opening and closing have therefore been arranged at the point inside the pyrolysis plant where the sieve medium is placed.

The invention is illustrated by the following special example, without limiting the scope thereof.

This example is shown in the figure. The cooler inlet head (1) is attached to the tube sheet, (2) by flange or connecting means not shown. The screen cage (4) stands on feet (3) on said tube sheet (2). Bars (5) are fixed within the cage (4) holding a plate cone (6). The cage (4) is upwardly tapered ending in an inlet nozzle (7). Said inlet nozzle (7 may be sealed to the inlet pipe or conduit (8) of said cooler inlet head (I) by means not shown. Inlet pipe (8) is flanged or disconnectably attached to inlet head (1) by a conventional disconnectable flange (12). The cage (4) consists of iron wire mesh with meshes of 6mm width and a wire thickness of 2mm. Said cage is reinforced by steel rings and steel bands, which arenot shown in the figure. The arrows indicate the approximate directions of the cracked gas stream. A major portion of the cracked gas that leaves hydrocarbon pyrolysis furnace (l0) enters via inlet pipe (8) andinlet nozzle (7) into the cage (4) which cage (4) comprises an inner truncated cone (4a) fitted upon an outer truncated cone (4b), each cone having different opening angles, passes through the cage meshes of the cage inner cone (42 into the space (9) intermediate the cage and the cooler inlet head (1), and from there this major portion of cracked gas returns into the cage outer cone 4b) and finally leaves the cage (4) via the bottom meshes to pass through the cooler (11), which latter is shown in the bottom of the figure. Flanges (l2) detachably connect inlet pipe or conduit (8) to cooler inlet head (1), and flanges (13) detachably connect the inlet head (1) to the cooler (11). Of the coke crusts formed on the wire occasionally larger pieces come off from the upper part of the cage (4) and fall to the bottom of said cage. In order to prevent these pieces from impeding the gas flow too strongly, the plate cone (6) has been provided for breaking the falling pieces. The embodiment as shown in this example was applied in an ethane pyrolysis plant. The cracked gases leaving the pyrolysis furnace (10) contain approximately 33 mole-% of ethene and have a temperature of 800 i 50 C. when entering the inlet pipe (8) of the cooler inlet head (I). When no sieve cage (4) was used, the plant had to be closed down about every 3 weeks because of coke obstructions. When it was used however, the only thing to do was to replace after 3 months the use cage by another coke-free one.

We claim:

1. An apparatus comprising a hydrocarbon pyrolysis furnace, a cooler having an inlet head, a conduit from said furnace to said cooler inlet head, means for disconnecting said inlet head from said conduit, means for inlet in said cooler inlet head conduit, and a cone fixedly mounted internally of said sieve cage with the apex of said cone being directed toward the inlet of said sieve cage.

v UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent no. 3,771,638 bated November 13, 1973 Invenmfls) Hans lE Richard Gustav Hussner; and

RaimunI Erhard Fischer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ABSTRACT, line 7, "line" should read t 1'. n g--. ABSTRACT, line 8, "stream" should rea' d -lS1in Col-1mm 2, line 38, "(42)" should read "E". I

Signd ar1dsea1ed this 30th day of Ju1y 1974.

(SEAL) Attest:

' MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

1. An apparatus comprising a hydrocarbon pyrolysis furnace, a cooler having an inlet head, a conduit from said furnace to said cooler inlet head, means for disconnecting said inlet head from said conduit, means for disconnectably attaching said cooler inlet head to said cooler, a perforated tube sheet secured to the interior surfaces of said inlet cooler head, a plurality of feet mounted on said tube sheet, a wire mesh sieve cage fixedly mounted on said plurality of feet and having an inlet in said cooler inlet head conduit, and a cone fixedly mounted internally of said sieve cage with the apex of said cone being directed toward the inlet of said sieve cage. 